It is well known that injection of a mixture of steam and flue gas into a hydrocarbon-bearing formation is used for increasing the production of hydrocarbons. Also, injection of gases at high temperatures into the hydrocarbon-bearing formation is used for the same purpose. This technique is very well described in the following U.S. Pat. No. 4,546,829; U.S. Pat. No. 3,948,323; U.S. Pat. No. 3,993,135; U.S. Pat. No. 2,734,578. This technique of affecting the hydrocarbon fluid present in the formation is realized by using primarily heat energy. However, the energy produced during combustion of such expensive and critical commodities, as hydrocarbon fuel, natural gas, products of oil refinery and recovered oil, is consumed to heat up the formation fluid.
Inert gases, such as, nitrogen, carbon dioxide, power plant exhaust gases are injected into a hydrocarbon-bearing formation to increase recovery of hydrocarbons.
The U.S. Pat. No. 4,330,038 offers to employ wet oxidation of combustible materials, as a source of energy and of production of a gas, which is to be injected into the formation. However, a part of energy, produced by the process of combustible materials wet oxidation, is consumed to support the process of wet oxidation, and, also, steam is used to produce energy. Consequently, the equipment for energy production is rather large and heavy.
The U.S. Pat. No. 5,402,847 describes a method of recovering methane from a coal bed by internal combustion engine exhaust gas injection into the coal bed, where methane is used as at least a part of fuel for a gas turbine engine or a diesel engine, and, where the exhaust gas is the exhaust gas of the gas turbine engine or the diesel engine. The gas, produced by this method from the coal bed, is a mixture comprising methane and inert gas, the inert gas comprising the exhaust gas components. In connection with this, the methane needs to be separated from the produced gas, and this operation requires additional expenses.
The U.S. Pat. No. 5,133,406 describes methane recovery from a coal seam by injecting fuel cell power system exhaust into the coal seam. Fluids, comprising methane, produced from the coal seam are further utilized in a fuel cell power system, which is very costly.
Injection of inert gas (such as, carbon dioxide, nitrogen, exhaust gas, and the like) into a hydrocarbon-bearing formation to increase recovery of hydrocarbons is accompanied by a significant increase of an amount of the produced gaseous component of a hydrocarbon-containing fluid, which is recovered from the formation. An increase of a gas factor (the term “gas factor” is explained below) is caused by inert gas breakthrough into production wells and by an increase of an amount of produced gaseous hydrocarbons, due to the inert gas ability to extract a part of gaseous hydrocarbons from a hydrocarbon-containing fluid present in the formation. For example, an increase of a gas factor was achieved, when formation oil-containing fluid was affected upon by carbon dioxide, and it resulted in 30-35% increase of the produced gaseous hydrocarbons amount and, accordingly, the value of the gas factor increased. Said 30-35% increase of the value of the gas factor has been achieved, due to the ability of the carbon dioxide to extract gaseous hydrocarbons from oil-containing fluid. An amount of gaseous hydrocarbons extracted from heavy oil (said oil, after its separation from formation oil-containing fluid has been affected upon by carbon dioxide) may be equal to an amount of gaseous hydrocarbons, separated from the formation oil-containing fluid /see: Mirsayapova, L. I. Extraction of light hydrocarbons from degassed oil under effect of CO2// Geology, oil recovery, physics and reservoir hydrodynamics/ Works TatNIPIneft. Kazan: Tatarskoye Publishing House, 1973, Vol. No. 22, p. 233, p. 236, p. 238; Vakhitov G. G., Namiot A. Yu., Skripka V. G. et al. Study of oil displacement with nitrogen on reservoir model at pressures up to 70 MPa. Neftianoye khozyastvo, 1985, No. 1, p. 37/. A considerably higher influence on the increase of the gas factor has the inert gas breakthrough into production wells. For example, the carbon dioxide concentration in the produced gaseous component (Schedel R. L in his article uses the term <<associated gas>>) can increase up to the levels of 90% after a period of 6 months of carbon dioxide injection. This means, that carbon dioxide breakthrough may result in increase of 5-10 times the volume of the produced gaseous component, containing up to 80-90% of carbon dioxide /see: Schedel R. L. EOR+CO2=A gas processing challenge. //Oil and Gas Journal, 1982, Vol. 80, N 43, Oct. 25, p. 158/.
Thus, inert gas injection into a hydrocarbon-bearing formation to increase recovery of hydrocarbons is inseparably connected with a significant increase of a hydrocarbon-containing fluid gaseous component production, and with an increase of an inert gas concentration in the produced gaseous component. Inert gas presence in the gaseous component worsens its quality, decreases a heating value of the gaseous component and an ability of the gaseous component to burn will deteriorate. Accordingly, using the gaseous component as gaseous fuel will be quite difficult.
A method for the production of pressurized nitrogen for injection application at high pressure is offered in the U.S. Pat. No. 4,895,710. Natural gas is combusted in air, the air is compressed prior to combustion. Carbon dioxide is removed from flue gas, and the remaining nitrogen is used for injection. Heat energy, produced during the natural gas combustion, is transformed into mechanical energy. The compression of the air prior to combustion was offered so as to reduce the equipment's mass. The produced nitrogen is offered to be used preferably for injecting into oil and natural gas formations. However, this method does not provide for the effective utilization of the produced gaseous component of a hydrocarbon-containing fluid, where the gaseous component is a mixture, comprising natural gas (for example, associated gas) and the injection nitrogen.
The article /Hlozek R. J. “Engine-Exhaust Gas Offers Alternative for EOR,” Oil and Gas Journal, Apr. 1, 1985, p.p. 75-78/describes exhaust gas injection into an oil-bearing formation. The exhaust gas production is described as the process of methane combustion in gas engines. Produced fluid is separated into oil and a gaseous component (the term “produced gas” is used in the article). Depending on the stage of the project's development, the gaseous component is injected into the formation and/or is sold as fuel gas. Also, natural gas liquids may be recovered from the gaseous component. However, there is no mentioning in the article about which methods and technical means would be employed to combust the gaseous component, which is sold as fuel gas. Together with this, the author declares, that when heating value of the produced gaseous fluid becomes lower than 950 BTU/cu ft (35,4×106 Joule/m3), nitrogen and carbon dioxide are removed from the gaseous component. This conditions the necessity of the nitrogen and carbon dioxide removal practically during the whole process of the project, which will require additional expenses for purchasing and maintenance of the necessary equipment.
W. B. Bleakley in his article describes, that flue gas is injected into an oil-bearing formation. A gaseous component (the author uses the term “gas stream”) of produced oil-containing fluid is separated from the fluid. The gaseous component is mixed with ethane and propane to increase heating value and then to be combusted in steam boilers, wherein the flue gas is produced. /Bleakley W. B., “Block 31 Miscible Flood Remains Strong,” Petroleum Engineer International, November, 1982, p.p. 84, 86, 90, 92/. The use of this technique requires the combustion of combustible substances with high heating value, which are quite expensive.
In the U.S. Pat. No. 1,729,300 it has been offered recovering an oil-containing fluid through at least one production well, separating a gaseous component of the fluid from the fluid in a separator and producing steam in a power plant. A part of steam is injected into the formation by an injection device (which is represented by a pump with a steam converter). Another part of steam is used to produce energy. A part of the heat energy produced in the power plant is consumed to increase oil recovery.
In the U.S. Pat. No. 4,007,786 the secondary oil recovery and fuel gas production by employing a fuel generator is described. A part of energy produced when combusting the fuel gas with air, is transformed into mechanical energy and/or electrical energy, and heat energy of exhaust gas is used to produce steam, which is injected into the formation. However, a part of the energy is consumed to produce the fuel gas in the fuel gas generator, and a part of energy is consumed to produce the steam injected into the formation, which leads to the increase of the energy consumption.
As it is described in RU Pat. No. 2,038,467, a gaseous component (the term “associated gas” is used) of an oil-containing fluid is separated from the fluid, recovered from an oil-bearing formation through at least one production well. The gaseous component is combusted with oxygen in a power plant and the produced exhaust gas, is injected into the formation.
As it is described in the U.S. Pat. No. 4,344,486, a mixture comprising hydrocarbon, hydrogen sulfide and carbon dioxide is combusted with an oxygen enriched gas to produce heat energy, and to produce a concentrated carbon dioxide stream, which is to be injected into a hydrocarbon-bearing formation, so as to increase the recovery of liquid hydrocarbons.
Methods and equipment, offered in the U.S. Pat. No. 4,344,486 and the RU Pat. No. 2,038,467, allow to produce heat energy and to quite simply realize the separation, because a gaseous component separated from a hydrocarbon-containing fluid may comprise any hydrocarbon in gaseous state. However, a volume of the gas, produced from the combustion of the gaseous component in oxygen, is approximately equal to a volume of the gaseous component. That is why, it is necessary to additionally supply gas from exterior sources for the injection into the formation. Also, oxygen (or the oxygen enriched gas) is quite expensive, and the production of the oxygen, (or, the oxygen enriched gas) is connected with the extra energy losses.
It is an object of this invention to provide a method and system for recovery of hydrocarbons from a hydrocarbon-bearing formation, wherein, the disadvantages and deficiencies of known methods and systems for recovery of hydrocarbons are overcome.
Another object of this invention is to provide a method and a system for recovery of hydrocarbons by means of gas injection into a hydrocarbon-bearing formation, wherein, an improved production of gas, to be used for injection into the formation, is realized, and wherein expensive separation equipment is not required.
It is still another object of this invention to provide a method and a system for recovery of hydrocarbons by means of gas injection into a hydrocarbon-bearing formation, wherein the method and the system are environmentally safer and energy efficient.
And, it is still another object of this invention to provide a method and a system for recovery of hydrocarbons by means of gas injection into a hydrocarbon-bearing formation, wherein, economical and energy efficient utilization of a gaseous component of a hydrocarbon-containing fluid, recovered from a hydrocarbon-bearing formation, is employed.
These and other objects and advantages of the present invention will undoubtedly become apparent to those skilled in the art from the following description, figures and claims.
The following terms, as used in the description and claims of the present invention, shall have the following meaning.
The term “hydrocarbon-containing fluid” is herein used to denote a fluid comprising any liquid and any gas, which comprises at least one gaseous hydrocarbon and from about 0 to about 90 mole percent of inert gas. A hydrocarbon-containing fluid may comprise solid particles. Oil, gas-condensate, water and the like, and also, their mixtures may be examples of a liquid contained in a hydrocarbon-containing fluid. Any gaseous hydrocarbon (for example, such as, methane, ethane, propane, propylene, butane or the like) or a mixture of gaseous hydrocarbons may be contained in a hydrocarbon-containing fluid. A hydrocarbon-containing fluid is recovered from a hydrocarbon-bearing formation. For example, a hydrocarbon-containing fluid may be recovered from an oil-bearing formation, or for example, from a gas-condensate reservoir, or from a natural gas reservoir, or the like.
The term “gaseous component of a hydrocarbon-containing fluid” or the term “gaseous component” is used to denote a component of a hydrocarbon-containing fluid, which said component comprises at least one gaseous hydrocarbon (for example, such as, methane, ethane, propane, butane or the like), and, from about 0 to about 90 mole percent of inert gas (for example, such as, carbon dioxide, nitrogen, exhaust gas or a mixture of carbon dioxide and nitrogen). A gaseous component of a hydrocarbon-containing fluid may be separated from the fluid and may comprise sulphur-containing substances, vapor, solid particles and other substances.
The term “liquid component of a hydrocarbon-containing fluid” is used to denote a component of a hydrocarbon-containing fluid, which said component comprises at least one liquid, for example, any liquid hydrocarbon, water and the like. Also, oil, gas-condensate, a mixture of oil and water, and, the like may be examples of a liquid contained in a liquid component of a hydrocarbon-containing fluid. A liquid component of a hydrocarbon-containing fluid may be separated from the fluid.
The term “air” is used to denote atmospheric air, or a similar gaseous mixture, for example, a gaseous mixture comprising between about 20 and 25 volume percent of oxygen, and between about 75 and 80 volume percent of nitrogen. In addition to free oxygen and nitrogen, this gaseous mixture may comprise water vapor, inert gas (for example, such as, argon and carbon dioxide) and others constituents, which are the like of constituents atmospheric air.
The term “inert gas” is herein used to denote any gas, which is not able to promote and to support combustion. Examples of inert gases include carbon dioxide, nitrogen, exhaust gas, argon, and the like, and, also, mixtures of these gases. “Inert gas” is preferably used to denote any gas selected from the group consisting of carbon dioxide, nitrogen, exhaust gas, and a mixture of carbon dioxide and nitrogen.
The term “exhaust gas” is used to denote a gaseous mixture, which results from combustion of a gaseous fuel with an oxidant. An oxidant may consist of air. An exhaust gas, resulting from combustion of a gaseous fuel with air, comprises nitrogen and carbon dioxide, if the gaseous fuel comprises at least one hydrocarbon. In addition to carbon dioxide and nitrogen, an exhaust gas may comprise oxygen, nitrogen oxides, water vapor, mechanical contaminants and other constituents.
The term “gas factor” is the ratio of a volume of produced gas to a volume of produced liquid hydrocarbons (for example, such as, oil, or gas-condensate, or the like), both are determined under standard conditions.
The term “power plant” is used to denote: 1) any device capable of generating energy by combusting a fuel, for example, such as, an internal combustion engine; or 2) an equipment combination capable of generating energy by combusting a fuel. For example, mechanical, or electrical, or heat energy, or any combination thereof, may be generated in a power plant by combusting a fuel.
The term “gas engine” is used to denote an internal combustion engine, which is capable of operating by combusting a gaseous fuel with air. Preferably the term “gas engine” is used to denote any internal combustion engine of piston type, which is capable of operating by combusting gaseous fuel with air. A spark-ignition engine capable of operating on gaseous fuel may be an example of a gas engine, and which, for example, may be a four-stroke, or a two-stroke type. Also, an example of such engine may be the Wankel engine, adapted to operate on gaseous fuel. The term “gas engine” is not used to denote a gas turbine engine. The term “gas engine” is not used to denote a gas-diesel engine.
The term “gas turbine engine” is used to denote an internal combustion engine comprising a gas turbine, which is capable to be driven by the expanding products of combustion of a gaseous fuel with air.
The term “gas-diesel engine” is used to denote an internal combustion engine which is capable of operating by combusting a gaseous fuel with air, but with injection of a small portion of liquid fuel to promote ignition only.
Also, we shall denote the following properties of gaseous hydrocarbons:                volume heating value of gaseous hydrocarbons, when they are being compressed, increases practically in proportion with pressure /see: Chugunov M., Khomich A. Handbook of a gas industry specialist. Transportation and use of natural liquefied gases., Minsk, Nauka I Technika, 1965, p. 23/. The term “volume heating value”, as used herein, shall denote heat amount value divided by fuel volume value, wherein the heat amount is produced from the complete combustion of the fuel;        increase of pressure of a hydrocarbon-air mixture widens its limits of flammability. For example, natural gas and atmospheric air mixture limits of flammability widen approximately twice as much, when pressure is increased from 0.1 MPa to 1 MPa /see: Lewis B., Elbe G. Combustion, flames and explosions of gases.—Moscow: Mir, 1968, p. 575/;        the gaseous hydrocarbons combustion reaction rate is in proportion with pressure /see: Isserlin A. S. The basics of gaseous fuel combustion. Leningrad: Nedra, 1987, p. 64/. That is, when the pressure is increased, burning rate of fuel, comprising gaseous hydrocarbons, increases and, accordingly, an amount of the fuel that may be combusted per time unit is increased also.        